ptk, the relationship of head diameter to shank diameter would depend on the size of the countersink. the deeper you go, the wider the head and it doesnt really make any difference what the sizes are. of course if a guy went real big, the wire might work harden before getting it peened properly, but within reason it shoud be ok. on many inlays i hold them with small wood screws. put them in after countersinking the inlay, but make it shallow enough that after filing screw to the level of the inlay, the screw slot is removed, making it appear as a pin. before installing the screw i put a drop of superglue in the screw hole. a person could do that with brass screws, also, or even silver if you can find any, i have never seen silver screws that i remember. as far as the counter sink, i use one that i think is 5/8 diameter but ends in a point, get them at home depot, lowes etc. mark